Utilizing spent mushroom substrate biochar to improve Zea mays L. growth and biochemical resilience against cadmium and chromium toxicity

Abstract

Heavy metal contamination in agricultural soils is a growing environmental concern, particularly due to the increasing accumulation of cadmium (Cd) and chromium (Cr) from industrial discharge, wastewater irrigation, and excessive fertilizer use. These toxic metals severely impact crop productivity by disrupting nutrient uptake, damaging root structures, and inducing oxidative stress, which collectively inhibit plant growth and development. Maize (Zea mays L.), a globally important cereal crop, is highly susceptible to heavy metal toxicity, making it essential to develop cost-effective and sustainable mitigation strategies. Spent mushroom substrate (SMS) biochar has emerged as an effective and sustainable method due to its ability to absorb heavy metals. Spent mushroom substrate biochar improves compost quality, soil fertility, and health. Its high porosity and surface area immobilize toxic metals, reducing nutrient losses and oxidative stress in plants. Pyrolysis temperature affects its surface area, nutrient composition, and adsorption abilities. This study aims to address this gap by evaluating the effectiveness of SMS biochar at varying application rates in mitigating Cd and Cr toxicity in maize. By assessing key physiological and agronomic parameters, this research provides novel insights into the potential of SMS biochar as a sustainable soil amendment for heavy metal-contaminated soils. Five treatments, i.e., 0, 50, 100, 150 and 200B were applied under Cd and Cr toxicity in 3 replications following the completely randomized design (CRD). Results exhibited that 200B caused an increase in maize plant height (26.1%), root dry weight (99.7%), grain yield (98.2%), and chlorophyll contents (50%) over control under Cd and Cr stress. In conclusion, 200B can mitigate Cd and Cr stress in maize plants. More investigations are suggested to declare 200B as a promising amendment for mitigation of Cd and Cr stress in other crops.

Keywords: Antioxidant; Biochar; Cadmium chromium; Chlorophyll content; Mushroom substrate.

Fig. 1

Effect of variable doses (control having Cd-Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize plant height (A), root dry weight (B), grains/cob (C) and grain yield (D) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 2

Effect of variable doses (control having Cd–Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize biological yield (A), chlorophyll (SPAD) (B), peroxidase (POD) (C) and superoxide dismutase (SOD) (D) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 3

Effect of variable doses (control having Cd–Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize ascorbate peroxidase (APX) (A), glutathione reductase (GR) (B) and glutathione (GSH) (C) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 4

Effect of variable doses (control having Cd-Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize ascorbic acid (AsA) (A), proline (B) and phenolics (C) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 5

Effect of variable doses (control having Cd-Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize root Cd (A), shoot Cd (B) and grains Cd (C) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 6

Effect of variable doses (control having Cd-Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize root Cr (A), shoot Cr (B) and grains Cr (C) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 7

Effect of variable doses (control having Cd–Cr but no B = 0 g), 50, 100, 150 and 200 g) of spent mushroom substrate derived biochar (B) on maize translocation factor of Cr from root to shoot (A), translocation factor of Cr from shoot to grains (B), translocation factor of Cd from root to shoot (C) and translocation factor of Cd from shoot to grains (D) cultivated under chromium and cadmium toxicity. Bars are means of 3 replicates ± SE. Variable bar letters showed significant changes at p ≤ 0.05 compared by Fisher’s LSD.

Fig. 8

(A) FTIR spectrum of spent mushroom substrate-derived biochar (SMS-B), showing characteristic absorption peaks at 3417–3423 cm⁻¹ (O–H stretching), 1618 cm⁻¹ (C = C and C = O stretching in aromatic rings), and 1045 cm⁻¹ (C–O stretching). (B) XRD pattern of SMS-B, indicating the presence of crystalline minerals such as SiO₂, CaCO₃, KCl, and CaSO₄, with distinct peaks around 25.5, 30°, and other relevant 2θ positions.